This invention generally relates to the field of semiconductor devices, and more particularly, is directed to a semiconductor device having a novel electrode lead composition.
A semiconductor device 10 typical of those known in the prior art is shown in FIG. 1. The device comprises two rows of in-line electrode leads 11, mounting island 11a, semiconductor chip 13, mounting past 12 and housing 15 molded from a resin compound. Chip 13 is mounted on island 11a with mounting paste 12 with each of its terminals (not shown) connected to respective electrode leads 11 by bonding wire 14. Bonding wire 14 is made of gold or other metals known in the prior art.
In semiconductor devices known in the prior art, such as device 10 shown in FIG. 1, electrode leads 11 and island 11a are made of so-called alloy 42 which consists of 42 wt percent of nickel (Ni) and 58 wt percent of iron (Fe). The thermal expansion coefficient of alloy 42 is very different from that of the resin compound used to mold housing 15, i.e., about 5.times.10.sup.-6 1/.degree.C. for alloy 42 as compared to 20.times.10.sup.-6 1/.degree.C. for the resin compound. Thus, when semiconductor device 10 is exposed to temperature variations, the dissimilar thermal expansion rates between alloy 42 and the resin compound will cause housing 15 to warp as indicated by upwardly concave portion 17. Cracks 16 may also form at the edges of mounting island 11a. Warping and the occurrence of cracks became more pronounced as the size of chip 13 and island 11a is increased.
Other kinds of metal alloys may also be used to form electrode leads 11 and island 11a. For example, so-called alloy 194 which consist of 97 wt percent of copper and 2.3 wt percent of iron. This alloy has a thermal expansion coefficient of 17.times.10.sup.-6 1/.degree.C. which is close to the thermal expansion coefficient for the resin compound used to mold housing 15. The thermal expansion coefficient of alloy 194, however, is very different from that of semiconductor chip 13 which has a thermal expansion coefficient of 3.times.10.sup.-6 1/.degree.C. Thus, when device 10 is exposed to temperature variations, the dissimilar thermal expansion rates between alloy 194 and silicon chip 13 will cause mounting island 11a and chip 13 to deform as shown in FIG. 2. When deformation occurs, chip 13 may crack or be peeled away from mounting island 11a.
Other kinds of iron alloys for electrode leads 11 and mounting island 11a have not been used in the prior art because of their lack of resistance to corrosion.